The total thickness of the Huronian Rocks in Canada is estimated as being not less than 18,000 feet, but there is considerable doubt as to their precise geological position. In their typical area they rest unconformably on the edges of strata of _Lower_ Laurentian age; but they have never been seen in direct contact with the _Upper_ Laurentian, and their exact relations to this series are therefore doubtful. It is thus open to question whether the Huronian Rocks constitute a distinct formation, to be intercalated in point of time between the Laurentian and the Cambrian groups; or whether, rather, they should not be considered as the metamorphosed representatives of the Lower Cambrian Rocks of other regions. As regards the fossils of the Huronian Rocks, little can be said. Some of the specimens of _Eozoön Canadense_ which have been discovered in Canada are thought to come from rocks which are probably of Huronian age. In Bavaria, Dr Gümbel has described a species of _Eozoön_ under the name of _Eozoön Bavaricum_, from certain metamorphic limestones which he refers to the Huronian formation. Lastly, the late Mr Billings described, from rocks in Newfoundland apparently referable to the Huronian, certain problematical limpet-shaped fossils, to which he gave the name of _Aspidella_. LITERATURE. Amongst the works and memoirs which the student may consult with regard to the Laurentian and Huronian deposits may be mentioned the following:[10]-- (1) 'Report of Progress of the Geological Survey of Canada from its Commencement to 1863,' pp. 38-49, and pp. 50-66. (2) 'Manual of Geology.' Dana. 2d Ed. 1875. (3) 'The Dawn of Life.' J. W, Dawson. 1876. (4) "On the Occurrence of Organic Remains in the Laurentian Rocks of Canada." Sir W. E. Logan. 'Quart. Journ. Geol. Soc.,' xxi. 45-50.' (5) "On the Structure of Certain Organic Remains in the Laurentian Limestones of Canada." J. W. Dawson. 'Quart. Journ. Geol. Soc.,' xxi. 51-59. (6) "Additional Note on the Structure and Affinities of Eozoön Canadense." W. B, Carpenter. 'Quart. Journ. Geol. Soc.,' xxi. 59-66. (7) "Supplemental Notes on the Structure and Affinities of Eozoön' Canadense," W. B. Carpenter, 'Quart. Journ. Geol. Soc.,' xxii. 219-228. (8) "On the So-Called Eozoönal Rocks." King & Rowney. 'Quart. Journ. Geol. Soc.,' xxii. 185-218. (9) 'Chemical and Geological Essays.' Sterry Hunt.